In what was most likely his final appearance at Celtic Park, 40-year-old Robert Douglas was sadly culpable for the 13th-minute goal which gave his former club a 1-0 half-time advantage.

It undermined an otherwise enterprising first-half display from Dundee, watched from the directors’ box by new interim manager John Brown, and they were further undone by another of their most experienced players after the break.

Just four minutes after appearing as a substitute, Matt Lockwood conceded a penalty kick and was sent off to pave the way for a second-half romp by Neil Lennon’s men.

The finishing line is now in clear sight for Celtic who require a maximum of just 13 points from their remaining 10 league fixtures to retain their crown.

But before Douglas committed the error which handed Celtic the lead, the home side were fortunate not to be punished for a mistake by their own goalkeeper at the other end.

Since returning from his recent neck injury, Fraser Forster has yet to recapture the exceptional form which illuminated the first half of his team’s season. The big Englishman looked far from convincing in the fifth minute here when his error seemed to have given Dundee a shock advantage.

Gary Harkins, the most eye-catching player on view for the visitors in the first half, whipped over a free-kick from the left which Forster could only fumble into the net at his near post. But the celebrations of the Dundee players were cut short by assistant referee Michael Banks’ flag, the official spotting that John Baird had edged narrowly offside as he made a run towards the post where Forster blundered.

There was no such reprieve for Dundee when Douglas was fully punished for his poor handling eight minutes later. Celtic created space smartly down the left through an exchange of passes between Emilio Izaguirre and Anthony Stokes, but Douglas should have dealt comfortably with the Honduran full-back’s cross.

Instead, he spilled the ball into the path of Joe Ledley who gratefully tapped in his fifth goal of the season from around six yards out.

Celtic, showing five changes to the starting line-up which drew at St Johnstone in midweek, looked to build on the breakthrough and exert the dominance expected of them against opponents 45 points behind them at kick-off. They almost grabbed a rapid second goal, but James Forrest scuffed his close-range shot from Gary Hooper’s cross and Douglas was able to block it.

But Dundee remained ambitious and competitive for the rest of the first half, threatening to equalise on more than one occasion. Declan Gallagher wastefully headed wide from Jim McAllister’s corner, while Harkins was desperately frustrated to see a deflected shot off Efe Ambrose superbly touched over by Forster, before heading against the crossbar from the resulting corner.

With Gary Hooper uncharacteristically wayward in front of goal, passing up a couple of premium opportunities, Celtic had to settle for their 1-0 lead at the break. But Lockwood’s fateful introduction to proceedings at the start of the second half, as a replacement for Brian Easton, wiped out any prospect of Dundee staging a recovery.

The veteran English defender blatantly fouled Hooper just as the striker was about to latch onto a Forrest cross inside the six-yard box. It was a simple decision for referee Kevin Clancy who awarded the penalty kick and showed a straight red card to Lockwood for denying a clear goalscoring opportunity.

With first-choice spot-kick taker Kris Commons not on duty, Forrest grabbed the ball and calmly sent Douglas the wrong way to make it 2-0. It was effectively game over and just a question of how successful the remaining 10 Dundee players could be in terms of damage limitation.

It soon resembled a glorified training exercise for Celtic as they knocked the ball around neatly in pursuit of gaps in Dundee’s enforced rearguard action. Anthony Stokes was linking play up cleverly for the home side and he created their third goal in the 57th minute. His cross from the left picked out Dylan McGeouch at the far post and the 20-year-old intelligently headed the ball back across goal and beyond Douglas’ right hand into corner of the net.

Stokes, whose own search for what would have been a deserved goal was denied by a fine Douglas save, was the provider again when Celtic made it 4-0. The Irishman cut the ball back into the path of Ledley who drove home a firm left foot shot via the underside of the crossbar from eight yards.

Ledley, captain once more in the absence of Scott Brown, completed a fine individual display by setting up Celtic’s fifth in the 83rd minute. The Welshman’s superb lofted pass found Hooper, who rediscovered his deadly touch by ramming home his 24th goal of the season from close range.